Oil-Gas Well Structure for Facilitating Extracting a Downhole Filter String and Method for Extracting the String

ABSTRACT

An oil-gas well structure for facilitating extracting a downhole filter string and a method for extracting the downhole filter string from the oil-gas well are provided. The oil-gas well structure includes a borehole wall ( 1 ) of the oil-gas well and a downhole filter string ( 2 ) run into the oil-gas well. The end of the downhole filter string ( 2 ) close to a wellhead is fixedly connected with the borehole wall ( 1 ). An annulus is formed between the downhole filter string ( 2 ) and the borehole wall ( 1 ), and the annulus is filled with ultra light particles, wherein, the density of ultra light particles approaches or is equal to the density of the carrier fluid which carries the ultra light particles. The method for extracting the downhole filter string includes the following steps: 1) establishing channels; 2) injecting the carrier fluid for ultra light particles so as to remove the ultra light particles from the annulus completely; 3) extracting the downhole filter string. The structure can conveniently extract the downhole filter string from the oil-gas well, thus facilitating the replacement and maintenance of the downhole filter string and the parameter regulation of a flow-control filter.

TECHNICAL FIELD

The present invention relates to the oil exploitation field, and specifically relates to an oil-gas well structure for facilitating extracting a downhole filter string and a method for extracting the downhole filter string from the oil-gas well. The oil-gas well here refers to a production well in a broader sense in oil-gas field development, which includes an oil well, a gas well, a natural gas well, an injection well, etc.

BACKGROUND ART

The completion structure of most mechanical sand control oil-gas wells comprises an oil-gas well and a downhole filter string run into the oil-gas well. The oil-gas well includes a vertical well, a deviated well, a highly-deviated well and a horizontal well. As shown in FIG. 1, the reference sign 1 in FIG. 1 indicates a borehole wall of an oil-gas well, the reference sign 2 indicates a downhole filter string, the reference sign 3 indicates an annulus between the downhole filter string and the borehole wall, the reference sign 4 indicates a packer for hanging the downhole filter string. The downhole filter string here is a downhole filter string in a broader sense and has a plurality of forms. For instance, in a first circumstance there is a downhole filter string having no flow-restriction function, which serves as only a sand control filter, and which is also called as a sand control screen. In a second circumstance, there is a filter having a flow-control function, i.e., a flow-control filter string, which is also called as a flow-control screen. The flow-control filter has a flow-control function, and at the same time has a filtering function, which function is sometimes to prevent an anti-channeling particle medium outside the flow-control filter from entering a wellbore, and which also has the function of preventing formation sand from entering the wellbore, for a sand production well. The flow-control function of the flow-control filter embodies a flow-restriction function as well.

The downhole filter string refers to a string formed by connecting one or more downhole filters in series. For example, a sand control screen with a total length of 300 meters, which is placed into a horizontal well, is formed by connecting 30 sand control screens of about 10 meters in series.

In an oil-gas well containing the downhole filter string, there exists the following two circumstances outside the downhole filter string: one circumstance in which outside the downhole filter string there are artificially filled gravels, which include quartz sand or ceramsites; the other circumstance in which outside the downhole filter string there are no fillers. If there are no fillers outside the downhole filter string, after a period of production by a sand production well, the produced formation sand may also fill up the annulus between the downhole filter string and the borehole wall, as shown in FIG. 1. The reference sign 5 in FIG. 1 represents formation sand or artificially filled gravels accumulated outside the downhole filter string. Both naturally filled formation sand and artificially filled gravels produce a great resistance for pulling a downhole filter string, such that it is difficult to extract a downhole filter string in an oil-gas well. In particular, for a well having a long downhole filter string, such as a highly-deviated well and a horizontal well, it is almost impossible to extract a downhole filter string.

However, it is necessary to extract a downhole filter string under a number of circumstances, such as the following several circumstances:

1. When it is necessary to repair a damaged downhole filter string, or to replace a downhole filter string;

2. When it is necessary to recycle extracted downhole filter strings so as to save much expenditure; and

3. When a flow-control filter string is used, the extraction of a flow-control filter string in the production process may facilitate conveniently regulating the flow-control parameters of the flow-control filter string such as to adapt to the flow requirements of different exploitation stages and improve the production efficiency of an oil-gas well.

At present, there is still no oil-gas well structure that facilitates extracting a downhole filter string, nor is there a particularly effective method for extracting a downhole filter string from an oil-gas well.

SUMMARY OF THE INVENTION

The technical problem required to be solved by the present invention is to provide an oil-gas well structure facilitating extraction of a downhole filter string and a method for extracting a downhole filter string from an oil-gas well.

In order to solve the aforementioned problem, the present invention uses the following technical solution:

The oil-gas well structure for facilitating extraction of a downhole filter string of the present invention comprises a borehole wall and a downhole filter string installed into the oil-gas well. One end of the downhole filter string close to the wellhead is an upper end of the filter string and is fixedly connected with the borehole wall. An annulus is formed between the downhole filter string and the borehole wall. The annulus between the downhole filter string and the borehole wall is filled with ultra-light particles. A density of the ultra-light particles approaches or is equal to a density of a carrier fluid for carrying the ultra-light particles. The carrier fluid for carrying the ultra-light particles is a liquid for carrying and conveying the ultra-light particles into the annulus, or for backwashing and conveying the ultra-light particles out of the annulus.

The ultra-light particles and the carrier fluid for the ultra-light particles have a density difference within a range of from −0.35 to +0.35, which range contains these two endpoint values.

Preferably, the ultra-light particles and the carrier fluid for the ultra-light particles have a density difference within a range of from −0.3 to +0.3, which range contains these two endpoint values.

The ultra-light particles are particles having an average particle diameter of 0.05-1.2 mm and a real density of 0.7-1.3 g/cm³.

Preferably, the ultra-light particles are particles having an average particle diameter of 0.05-0.8 mm and a real density of 0.94-1.08 g/cm³.

Preferably, the ultra-light particles are macromolecule polymer particles.

Preferably, the ultra-light particles are high density polyethylene particles having an average particle diameter of 0.05-0.8 mm and a real density of 0.90-0.98 g/cm³.

Alternatively, the ultra-light particles are polypropylene and PVC macromolecule polymer particles having an average particle diameter of 0.05-0.8 mm and a real density of 0.7-1.3 g/cm³.

Alternatively, the ultra-light particles are styrene and divinylbenzene cross-linked copolymer particles having an average particle diameter of 0.05-0.8 mm and a real density of 0.94-1.08 g/cm³.

The present invention also discloses a method for extracting a downhole filter string from an oil-gas well structure for facilitating extraction of a downhole filter string, which method includes the following steps:

1) Establishing channels by opening an annulus between an upper end of a downhole filter string and a borehole wall;

2) Removing ultra-light particles using a carrier fluid for backwashing by injecting a carrier fluid for ultra-light particles into the downhole filter string in order to backwash and carry the ultra-light particles away from the annulus;

3) Extracting the downhole filter string.

When the downhole filter string is a flow-control filter string, the step of removing ultra-light particles by a carrier fluid for backwashing is in a way such as to connect a fluid injection pipe with the downhole filter string and directly inject the carrier fluid for ultra-light particles into the flow-control filter string. Due to a flow-control effect of the flow-control filter string, the injection fluid is uniformly injected into the ultra-light particles from various segments of the flow-control filter string, and the ultra-light particles that are accumulated outside the downhole filter string are removed by means of an upper fluid flow passage of the downhole filter string.

When the downhole filter string is a flow-control filter string, the step of removing ultra-light particles by a carrier fluid for backwashing is in a way such as to run a fluid injection pipe into the downhole filter string, the fluid injection pipe being used to perform fluid injection. A lower portion of the fluid injection pipe has an opening an upper portion of which is provided with a seal ring having an outside diameter substantially identical to an inside diameter of the downhole filter string. The fluid injection is performed in a sectional manner, with the fluid injection pipe being gradually run into a bottom of the downhole filter string for sectional fluid injection and sectional removal of ultra-light particles outside the downhole filter string from the top of the downhole filter string. When the ultra-light particles outside an anterior segment of the downhole filter string close to a wellhead are removed, the fluid injection pipe is penetrated into the downhole filter string for another segment until those particles outside the downhole filter string are completely removed. Alternatively, it is possible to continuously move the fluid injection pipe to perform fluid injection until the ultra-light particles outside the downhole filter string are removed.

When the downhole filter string is a downhole filter string having no flow-restriction function, the step of removing ultra-light particles by a carrier fluid for backwashing is in a way such as to run a fluid injection pipe into the downhole filter string, the fluid injection pipe being used to perform fluid injection. A lower portion of the fluid injection pipe has an opening an upper portion of which is provided with a seal ring having an outside diameter substantially identical to an inside diameter of the downhole filter string, with the fluid injection being performed in a sectional manner. The fluid injection pipe is gradually penetrated into a bottom of the downhole filter string for sectional fluid injection and sectional removal of ultra-light particles outside the downhole filter string from the top of the downhole filter string. When the ultra-light particles outside an anterior segment of the downhole filter string close to the wellhead are removed, the fluid injection pipe is penetrated into the downhole filter string for another segment until those particles outside the downhole filter string are completely removed. The fluid injection pipe may be moved in a manner such as to continuously move the fluid injection pipe to perform fluid injection until the ultra-light particles outside the downhole filter string are removed.

Preferably, the carrier fluid for ultra-light particles as defined in the present invention is water or a water solution.

The present invention utilizes a carrier fluid for ultra-light particles having a density of about 1 g/cm³ and uses ultra-light particles having a real density very close to that of the carrier fluid so that the carrier fluid may easily carry the ultra-light particles for filling into an annulus between the downhole filter string and the borehole wall, filling in and filling up the annulus between the downhole filter string and the borehole wall. A part of the carrier fluid enters the downhole filter string and returns to the ground surface and a further part of the carrier fluid penetrates into the formation through the borehole wall. Finally, a completion structure is formed in which ultra-light particles fill up the annulus between the downhole filter string and the borehole wall.

At the same time, the ultra-light particles occupy the space of the annulus between the downhole filter string and the borehole wall, and also obstruct the accumulation of formation sand in the space of the annulus between the downhole filter string and the borehole wall.

The present invention uses particles having an average particle diameter of 0.05-1.2 mm and a real density of 0.7-1.3 g/cm³ as ultra-light particles for filling the annulus between the downhole filter string and the borehole wall. When it is necessary to extract the downhole filter string, it is possible to easily remove the ultra-light particles that have accumulated outside the downhole filter string. Because the density of the ultra-light particles is very close to that of the carrier fluid, the carrier fluid circulating in a low speed may conveniently take the ultra-light particles to the ground and remove the ultra-light particles in the annulus outside the downhole filter string, so that the downhole filter string may be conveniently extracted from the oil well. The requirements for extracting a downhole filter string thus are satisfied.

The method as defined in the present invention, which is easy to carry out, overcomes the difficulties in extracting a downhole filter string in an oil well and thus facilitates the production. Moreover, the removed ultra-light particles may be recycled, thereby greatly reducing production costs.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a completion structure as defined in the Background Art.

FIG. 2 is a view of a completion structure as defined in Embodiment 1 of the present invention.

FIG. 3 is a view of a flow path of carrier fluid for backwashing and removing ultra-light particles outside a filter string as defined in Embodiment 2 of the present invention.

FIG. 4 is a view of a flow path of carrier fluid for backwashing and removing ultra-light particles outside a filter string as defined in Embodiment 3 of the present invention.

FIG. 5 is a view of a flow path of carrier fluid for backwashing and removing ultra-light particles outside a filter string as defined in Embodiment 4 of the present invention.

FIG. 6 is a view of an oil-gas well structure after removing ultra-light particles as defined in the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Embodiment 1

As shown in FIG. 2, an oil-gas well structure for facilitating extraction of a downhole filter string as defined in the present invention comprises an oil-gas well borehole wall 1 and a downhole filter string 2 run into the oil-gas well. A packer 4 for hanging the downhole filter string is provided between one end of the downhole filter string close to the wellhead and the borehole wall. An annulus is formed between the downhole filter string and the borehole wall. The annulus between the downhole filter string and the borehole wall is filled with ultra-light particles 6.

Embodiment 2 A Method for Extracting a Flow-Control Filter String

In the completion structure as shown in FIG. 2 and as defined in Embodiment 1, the ultra-light particles are polypropylene and PVC macromolecule polymer particles having an average particle diameter of 0.05-0.8 mm and a real density of 0.7-1.3 g/cm³.

As shown in FIG. 3, the downhole filter string, which is a flow-control filter string 2, is provided with a flow-control filter 2-1. The method for extracting the downhole filter string is as follows:

1) Opening a packer for hanging the downhole filter string: For a packer unset by pulling, the opening method is in a way such that the packer is unset automatically when the packer is pulled. For a packer unset by rotating, the packer is unset automatically when the packer is rotated. Between the unset packer and the borehole wall there exists a gap, which becomes a fluid circulating passage.

2) Removing ultra-light particles by a carrier fluid for backwashing: Connect a fluid injection pipe with the downhole filter string and directly inject the carrier fluid for ultra-light particles into the flow-control filter string. Due to a flow-control effect of the flow-control filter string, the injection fluid is uniformly injected into the ultra-light particles from various segments of the flow-control filter string. In FIG. 3, the arrow directions indicate how the carrier fluid flows.

3) Removing: Ultra-light particles are taken out of the well by the carrier fluid until the ultra-light particles that accumulated outside the downhole filter string are removed. The structure of oil-gas well after removal is as shown in FIG. 6.

4) Extracting the downhole filter string.

Embodiment 3 A Method for Extracting a Control-Flow Filter String

In the completion structure as shown in FIG. 2 and as defined in Embodiment 1, the ultra-light particles are styrene and divinylbenzene cross-linked copolymer particles having an average particle diameter of 0.05-0.8 mm and a real density of 0.94-1.08 g/cm³.

As shown in FIG. 4, the downhole filter string, which is a flow-control filter string 2, is provided with a flow-control filter 2-1. The method for extracting the downhole filter string is as follows:

1) Opening a packer for hanging the downhole filter string: For a packer unset by pulling, the opening method is in a way such that the packer is unset automatically when the packer is pulled. For a packer unset by rotating, the packer is unset automatically when the packer is rotated. Between the unset packer and the borehole wall there exists a gap, which becomes a fluid circulating passage.

2) Removing ultra-light particles by a carrier fluid for backwashing: Run a fluid injection pipe 7 into the downhole filter string, the fluid injection pipe 7 being used to perform fluid injection. A lower portion of the fluid injection pipe has an opening an upper portion of which is provided with a seal ring 8 having an outside diameter substantially identical to an inside diameter of the downhole filter string. The fluid injection is performed in a sectional manner. The fluid injection pipe is gradually penetrated into a bottom of the downhole filter string for sectional fluid injection and sectional removal of ultra-light particles outside the downhole filter string from a top of the downhole filter string. Due to an effect of the seal ring, the seal ring may block the carrier fluid injected into the downhole filter string by the fluid injection pipe at a lower side of the seal ring and thus concentrate the carrier fluid to impact parts deposited with ultra-light particles. When ultra-light particles outside an anterior segment of the downhole filter string close to a wellhead are removed, the fluid injection pipe is penetrated into the downhole filter string for another segment until those particles outside the downhole filter string are completely removed. This avoids the carrier fluid not affecting the deposited ultra-light particles and saves much carrier fluid. The arrow direction in FIG. 4 indicates a flow direction of the carrier fluid. The dotted line in FIG. 4 presents that the fluid injection pipe is gradually penetrated into the downhole filter string for sectional fluid injection. The fluid injection pipe may be penetrated into the downhole filter string in a continually uniform-speed penetrating manner. As the continually uniform-speed moving injection pipe gradually injects fluid, after ultra-light particles are removed the depth gradually increases until the ultra-light particles outside the downhole filter string are completely removed. The arrow direction in FIG. 4 indicates a flow method of the carrier fluid.

3) Removing: The ultra-light particles are taken out of the well by the carrier fluid until the ultra-light particles that accumulated outside the downhole filter string are removed. The structure of oil-gas well after removal is as shown in FIG. 6.

4) Extracting the downhole filter string.

Embodiment 4 A Method for Extracting a Downhole Filter String Having No Flow-Restriction Function

In the completion structure as shown in FIG. 2 and as defined in Embodiment 1, the ultra-light particles are high density polyethylene particles having an average particle diameter of 0.1-0.5 mm and a real density of 0.94 g/cm³.

As shown in FIG. 5, the downhole filter string is a downhole filter string 2 having no flow-restriction function. The method for extracting the downhole filter string is as follows:

1) Opening the annulus between one end of the downhole filter string close to the wellhead and the borehole wall, and establishing a fluid circulating passage at an upper portion of the annulus between one end of the downhole filter string close to the wellhead and the borehole wall: For a packer unset by pulling, the opening method is in a way such that the packer is unset automatically when the packer is pulled. For a packer unset by rotating, the packer is unset automatically when the packer is rotated. Between the unset packer and the borehole wall there exists a gap, which becomes a fluid circulating passage.

2) Removing ultra-light particles by a carrier fluid for backwashing: Run a fluid injection pipe 7 into the downhole filter string, the fluid injection pipe 7 being used to perform fluid injection. At the end of the fluid injection pipe there is provided a seal ring 8 having an outside diameter substantially identical to an inside diameter of the downhole filter string. A fluid outlet 9 of the fluid injection pipe is at a position slightly lower than the seal ring of the fluid injection pipe. The fluid injection is performed in a sectional manner, with the fluid injection pipe being gradually penetrated into a bottom of the downhole filter string for sectional fluid injection and sectional removal of ultra-light particles outside the downhole filter string from the top of the downhole filter string. Due to an effect of the seal ring, the seal ring may block the carrier fluid injected into the downhole filter string by the fluid injection pipe at a lower side of the seal ring inside the downhole filter string so that it is difficult for the carrier fluid to enter the upper side of the seal ring. At places where the ultra-light particles are removed at an upper side there is no more carrier fluid entering from the filter string, thus concentrating the carrier fluid to remove ultra-light particles that are required to be removed. When ultra-light particles outside an anterior segment of the downhole filter string close to a wellhead are removed, the fluid injection pipe is penetrated into the downhole filter string for another segment until those particles outside the downhole filter string are completely removed. This avoids the run-up of the carrier fluid and thus saves much carrier fluid and maintains a higher flow speed of impacting ultra-light particles. The arrow direction in FIG. 5 indicates a flow direction of the carrier fluid. The dotted line in the figure shows that the fluid injection pipe is gradually penetrated into the downhole filter string for sectional fluid injection. The fluid injection pipe may be penetrated into the downhole filter string in an intermittently penetrating manner. The intermittently moving injection pipe gradually injects fluid until the ultra-light particles outside the downhole filter string are completely removed.

3) Removing: The ultra-light particles are taken out of the well by the carrier fluid until the ultra-light particles that accumulated outside the downhole filter string are removed. The structure of oil-gas well after removal is as shown in FIG. 6.

4) Extracting the downhole filter string.

The carrier fluid as defined in Embodiments 2-4 may be water or a water solution added with common additives for an oil field.

The method as defined in the present invention, which is easy to carry out, overcomes the difficulties in extracting a downhole filter string in an oil well and thus facilitates production. Moreover, the removed ultra-light particles may be recycled, thereby greatly reducing production costs.

The density of the particles in the present patent refers to a real density of particles.

The present patent also covers a circumstance in which a thinner downhole filter string is secondarily run into an initial downhole filter string of a well that is already present with a downhole filter string. It covers circumstances in which a filter string is run into a casing perforated well, a well with a porous pipe and an open-hole well.

Finally, it is imperative to understand that the aforementioned embodiments only pertain to exemplifications made to clearly illustrate the present invention rather than definitions of the embodiments. On the basis of the descriptions, a person skilled in the art may also make changes or variations of other different forms. It is unnecessary and impossible to list all the embodiments; however, obvious changes or variations deriving therefrom still fall into the protection scope of the present invention. 

1-13. (canceled)
 14. An oil-gas well structure for facilitating extraction of a downhole filter string, the structure comprising: a borehole wall of an oil-gas well; and a downhole filter string installed in the oil-gas well, an upper end of the downhole filter string close to a wellhead being fixedly connected with the borehole wall, and an annulus being formed between the downhole filter string and the borehole wall, wherein the annulus between the downhole filter string and the borehole wall is filled with ultra-light particles having a density that approaches or is equal to a density of a carrier fluid for carrying the ultra-light particles, the carrier fluid being a liquid for carrying and conveying the ultra-light particles into the annulus or for backwashing and conveying the ultra-light particles out of the annulus.
 15. The oil-gas well structure for facilitating extraction of a downhole filter string according to claim 14, wherein the ultra-light particles are particles having an average particle diameter of 0.05-1.2 mm and a real density of 0.7-1.3 g/cm³.
 16. The oil-gas well structure for facilitating extraction of a downhole filter string according to claim 15, wherein the ultra-light particles are particles having an average particle diameter of 0.05-0.8 mm and a real density of 0.94-1.08 g/cm³.
 17. The oil-gas well structure for facilitating extraction of a downhole filter string according to claim 15, wherein the ultra-light particles are macromolecule polymer particles.
 18. The oil-gas well structure for facilitating extraction of a downhole filter string according to claim 15, wherein the ultra-light particles are high density polyethylene particles having an average particle diameter of 0.05-0.8 mm and a real density of 0.90-0.98 g/cm³.
 19. The oil-gas well structure for facilitating extraction of a downhole filter string according to claim 15, wherein the ultra-light particles are polypropylene and PVC macromolecule polymer particles having an average particle diameter of 0.05-0.8 mm and a real density of 0.7-1.3 g/cm³.
 20. The oil-gas well structure for facilitating extraction of a downhole filter string according to claim 17, wherein the ultra-light particles are styrene and divinylbenzene cross-linked copolymer particles having an average particle diameter of 0.05-0.8 mm and a real density of 0.94-1.08 g/cm³.
 21. The oil-gas well structure for facilitating extraction of a downhole filter string according to claim 14, wherein the ultra-light particles and the carrier fluid have a density difference within a range of from −0.35 to +0.35, the range including endpoint values of −0.35 and +0.35.
 22. The oil-gas well structure for facilitating extracting a downhole filter string according to claim 21, wherein the ultra-light particles and the carrier fluid have a density difference within a range of from −0.3 to +0.3, the range including endpoint values of −0.3 and +0.3.
 23. A method for extracting a downhole filter string from an oil-gas well structure for facilitating extraction of a downhole filter string, the structure including: a borehole wall of an oil-gas well, and a downhole filter string installed in the oil-gas well, wherein an upper end of the downhole filter string close to a wellhead is fixedly connected with the borehole wall, wherein an annulus is formed between the downhole filter string and the borehole wall, wherein the annulus between the downhole filter string and the borehole wall is filled with ultra-light particles having a density that approaches or is equal to a density of a carrier fluid for carrying the ultra-light particles, and wherein the carrier fluid is a liquid for carrying and conveying the ultra-light particles into the annulus or for backwashing and conveying the ultra-light particles out of the annulus, the method comprising steps of: establishing channels by opening an annulus between an upper end of a downhole filter string and a borehole wall; removing ultra-light particles from the annulus using a carrier fluid for backwashing, the carrier fluid being injected into the downhole filter string in order to backwash and carry the ultra-light particles away from the annulus; and extracting the downhole filter string.
 24. The method for extracting a downhole filter string according to claim 23, wherein the downhole filter string is a flow-control filter string, and wherein the step of removing the ultra-light particles includes connecting a fluid injection pipe with the downhole filter string and directly injecting the carrier fluid into the flow-control filter string.
 25. The method for extracting a downhole filter string according to claim 23, wherein the step of removing the ultra-light particles includes installing a fluid injection pipe into the downhole filter string to perform fluid injection, a lower portion of the fluid injection pipe having an opening, an upper portion of the fluid injection pipe above the opening being provided with a seal ring having an outside diameter substantially identical to an inside diameter of the downhole filter string, and the fluid injection being performed in a sectional manner.
 26. The method for extracting a downhole filter string according to claim 23, wherein the carrier fluid is water or a water solution. 